1. Technical Field
The invention relates to vehicle tires and particularly to a run flat pneumatic tire containing a thin annular band which acts as a structural compression member when the tire is in the unpressurized or uninflated state to enable the tire to run in the unpressurized condition. More particularly, the invention relates to a band element which is formed as a composite structure of a plurality of helically wound fiber tows contained in a resin matrix wherein a first group of the fiber tows are located adjacent the neutral axis of the band to provide increased interlaminar shear strength with a second group of fibers arranged adjacent the outer and inner surfaces of the band to create a high level of circumferential stiffness.
2. Background Information
Various tire constructions have been devised over the years which enable a tire to run in an under-inflated or non-inflated condition such as after receiving a puncture and loss of pressurized air for extended periods of time and at relatively high speeds. This enables the operator to safely drive the vehicle to an appropriate location for repair or replacement of the punctured tire. Certain of these safety tires, referred to as xe2x80x9crun flat tiresxe2x80x9d, have been successful for certain applications and certain types of tire constructions. Most of these run flat tires achieve their run flat capability, by the placement of reinforcing layers or members of relatively stiff elastomeric material in the side walls of the tire which enable the tire to support the vehicle weight even with the complete loss of internal air pressure. Examples of such prior art run flat tire constructions which use such sidewall inserts are shown in U.S. Pat. Nos. 3,911,987; 3,949,798; 3,954,131; 4,067,372; 4,202,393; 4,203,481; 4,261,405; 4,265,288; 4,287,924; 4,365,659; 4,917,164 ; and 4,929,684.
In addition to these prior art run flat tires, various run flat tire constructions have been developed which utilize a thin annular band which extends circumferentially throughout the tire beneath the tread area. Examples of such banded run flat tires are shown in U.S. Pat. Nos. 4,111,249; 4,318,434; 4,428,411; 4,459,167; 4,734,144 4,428,411; 4,673,014; 4,794,966 ; and 4,456,048.
Banded tires have been fabricated with band materials made of steel, aluminum, titanium, and epoxy and thermoplastic composites with glass, KEVLAR (aromatic polyamide) and graphite fiber reinforcement. The common failure mode with these lightweight, laminated band constructions is interlaminar shear along the band""s primary bending neutral axis. This is a fatigue failure and is directly related to the spectrum of cyclic operating stress. As in all fatigue failures, the lower the stress, the longer the operating life.
In summary, the present invention provides a band element for a run flat tire which has both increased interlaminar shear strength and increased circumferential strength or stiffness in order to reduce failure of the band by the use of two types of fiber tows embedded in the resin matrix of the band.
The present invention provides a band element for a run flat pneumatic tire which is formed as a composite containing at least two different groups or types of fiber tows encased in a resin matrix with one group of the fiber tows being located adjacent the neutral axis of the band to provide increased interlaminar shear strength and with a second group of the fiber tows being located adjacent the inner and outer surfaces of the band to provide increased circumferential stiffness.
Another aspect of the invention is to provide a band that features both the desired levels of bending stiffness and of shear strength that is sufficient to avoid interlaminar shear crack initiation and growth during both the normal and typical life of the inflated tire and also during the desired life of the tire when operated in the run flat condition. This is in contrast to many of the prior art banded tires which are designed to meet only one of the conditions and not of both of the conditions, while providing the necessary tire-to-ground contact zone for development of tractive control forces, the desired level of ride comfort, and acceptable level of generated noise.
Still another aspect of the invention provides forming the first group of fiber tows of twisted fibers oriented at an angle within a range of 20xc2x0 and 60xc2x0 with the second group of fiber tows being formed of twisted fibers twisted at an angle with a range of 0xc2x0 and 25xc2x0.
Another feature of the invention is to provide a band element in which a plurality of chopped fibers are interspersed between the layers of tows within the matrix, which fibers extend between the tow layers to increase interlaminar shear fatigue strength and laminate stiffness to resist the various peel stresses imparted thereon.
Another aspect of the invention is to form the fiber tows of fuzzy fibers which have a plurality of frayed fibers extending outwardly from the tows and crossing over into adjacent tows, again to increase the interlaminar shear strength and to resist peel stresses between the tow layers.
Still another aspect of the invention is to arrange the individual tows in a nesting relationship with the adjacent tows of adjacent layers in order to reduce the formation of resin only planes parallel to the band surface, which planar zones or areas are susceptible to cracking and interlaminar shear.
A further aspect of the invention is to provide a run flat band in which the two distinctly different groups of fibers are arranged in such a manner as to provide a gradual decrease in circumferential stiffness through the thickness of the band decreasing toward the central region of the band while at the same time there is a gradual increase in interlaminar shear strength towards the neutral axis of the band.
Thus, the present invention provides a band element which can be manufactured in an efficient and effective manner for subsequent incorporation into a run flat tire wherein the band has maximum interlaminar shear strength adjacent the neutral axis of the band which decreases gradually towards the inner and outer surfaces while providing maximum circumferential stiffness adjacent the inner and outer band surfaces which decreases gradually towards the center or neutral axis of the band.
The foregoing advantages, construction, and operation of the present invention will become more readily apparent from the following description and accompanying drawings.